ABSTRACT For over 20 years, health care delivery in the U.S. has been informed by methodologies that create ?service areas?, such as Hospital Service Areas (HSAs) of the Dartmouth Atlas Project, to evaluate how health care resources are distributed across the population and how that impacts health outcomes. Policy makers have used these units to assess regional variation in health care utilization and quality to design strategies for improving health and health care systems. Delivery of cancer care in the United States represents a unique set of patients, technologies, clinical specialization, and patient- centered perspectives, distinct from other patient populations. The Institute of Medicine and the American Society of Clinical Oncology have recently noted that there is a ?crisis? in cancer care delivery, and highlighted the need for meaningful ways to assess quality. We propose to develop a novel method to generate Cancer Service Areas (CSAs) ? geospatial units analogous to HSAs, but specific to cancer care ? in order to create a framework for assessing regional cancer care delivery, quality, and outcomes. Based on health care utilization captured through all-payer claims and Medicare claims, we will extend and refine the Dartmouth HSA model. The derived CSAs have several key distinctions from existing service area delineations: a) focus on cancer-specific patient population/diagnoses; b) inclusion of outpatient claims, in addition to inpatient, to capture continuum of care; c) refinement of a complex network-based community detection method to account for spatial patterns of patient care while attaining geographic contiguity of the CSAs; and d) creation of an automated program in a Geographic Information Systems (GIS) environment that adapts to user-defined sets of services, diagnoses, or clinical phenotypes. Our specific aims are to: 1) Develop Cancer Service Areas (CSAs)- unique, cancer-specific geographic units of healthcare utilization to evaluate cancer care through a refined methodologic approach; 2) Evaluate the CSAs versus Dartmouth HSAs to assess their spatial specificity to the population of interest; and 3) Demonstrate the utility of CSAs as unique spatial units with respect to the cancer population. Creation of CSAs is an urgent need for policymakers (e.g. Congress), decision leaders (e.g. ASCO), health care systems, and ultimately patients who seek reliable, reportable information on quality cancer care. It is a first step towards these goals, and promises to serve broad service area methodologies at the same time.